1. Field of the Invention
This invention relates to a torque nut for a mine roof bolt assembly in which the bolt is to be rotated through the nut after installation of the bolt in a mine roof bore hole using a mine bolt resin system to cause mixing of the resin.
2. Discussion of Related Technology
Mine roof bolt systems (such term being inclusive of rock bolt systems) are commonly set into a bore hole drilled into rock strata defining a mine roof using a mine bolt resin system that utilizes multi-components mixed in situ by rotation of the mine bolt after installation of the resin and bolt in the bore hole to thereby cause the resin to span the gap between the bolt and the mine roof bore hole and to retain the bolt firmly in the bore hole.
It is also common practice to transmit resin mixing torque to the mine roof bolt through a nut element to cause mixing of the resin system after the bolt has been inserted into the bore hole and to fracture the capsules or cartridges of the resin to cause the resin to flow into the area between the mine roof bolt and the surrounding walls of the bore hole in the mine roof.
The nut element used to rotate the bolt is the same nut element used to tension the bolt after the resin has cured and hardened so that it is important to control the degree of torque transmitted through the nut into the bolt along the nut and bolt threads so that, after the bolt has been set in the resin and the resin has hardened, the nut can be advanced along the bolt without excessive difficulty.
Power tools or pinners are typically used to drive the mine roof bolts into the bore holes placed in the rock of the mine roof and the pinners are also driven in rotation to apply torque to the nut elements associated with the mine roof bolts to thereby mix the resin previously inserted in the bore hole through the rotation of the mine bolt, followed by advancement of the nut along the mine roof bolt (after the resin has hardened) to tension the bolt in its bore hole while producing a thrust against a pressure plate or other element located between the nut and the mine roof.
Typical prior art examples are described in U.S. Pat. No. 4,662,795 granted to Clark et al. on May 5, 1987; and U.S. Pat. No. 5,352,065 granted to Arnall et al. on Oct. 4, 1994. In each of these examples, a torque nut applied to the mine roof bolt has a deformable or frangible portion that permits transmittal of a predetermined torque through the nut into the bolt to rotate the bolt and to cause mixing of the resin system that has been previously placed in the bore hole to secure the bolt in the mine roof before the nut is fully advanced along the bolt. The deformable and frangible sections of the torque nuts, however, tend to interfere with the power tools used to rotate the nuts and find their way into the pinners or the mine machinery used to drive the pinners.
Other torque nut arrangements are described in U.S. Pat. No. 5,417,520 granted to Rastall on May 23, 1995; 4,132,080 granted to Hansen on Jun. 2, 1979; 4,303,354 granted McWolell, Jr. on Dec. 1, 1981; 3,940,941 granted to Libert et al. on Mar. 2, 1976; and 3,877,235 granted Hill on Apr. 15, 1975.
Additional mine roof bolt systems are described in U.S. Pat. Nos. 4,607,984 granted to Cassidy on Aug. 26, 1986 and 4,275,975 granted to Morgan on Jun. 30, 1981.
The mine roof bolt systems and their associated nuts used to apply a controlled torque to the bolt elements have various disadvantages, including frangible portions as noted previously, non-uniform torque transmitting characteristics, stress concentrations localized along the nut or bolt threads and relatively high costs of production.